The present invention relates to a method of setting up a dialysis treatment in a dialysis machine.
In general, dialysis machines are preset for carrying out dialysis treatments that are personalized for patients affected by renal insufficiency. In other words, the dialysis machines have control devices that make it possible to set up a dialysis treatment that is specific to each patient on the basis of the medical instructions. As a rule, a prescription for a patient affected by renal insufficiency and undergoing dialysis treatment comprises instructions relating to the weight loss that the patient should experience and to the amount of salts that the patient should receive in the form of ions during the dialysis treatment. Other data characterizing the dialysis treatment, such as the maximum weight loss in unit time tolerated by the patient and the duration of the dialysis treatment, can be obtained from the general conditions of health and from the patient""s physical characteristics. The weight loss during a dialysis treatment is due to expulsion of a proportion of the blood fluid.
For this purpose, a dialysis machine of known type comprises an extracorporeal blood circuit connected, in use, to the patient""s circulatory system, a dialysate circuit, and a filter through which the blood circuit conveys the blood fluid and the dialysate circuit conveys the dialysate. The filter comprises a semipermeable membrane, which separates, in use, the dialysate from the blood fluid and permits an exchange of ions between the dialysate and the blood fluid and the transfer of a proportion of the blood fluid through the membrane. The machine further comprises an ultrafiltration pump for expelling a defined quantity of the patient""s blood fluid from the dialysate circuit and through the membrane to achieve the aforesaid weight loss. Therefore there is a biunique correspondence between the weight loss and the quantity of blood fluid expelled during the whole treatment and, similarly, between the weight loss in unit time, also called the rate of weight loss, and the delivery of the ultrafiltration pump. However, this correspondence is not valid in the case where the extracorporeal circuit is provided with an infusion bag that releases a flow of infusion fluid into the blood circuit. In this case the weight loss in unit time will be equal to the difference between the ultrafiltration flow rate and the infusion flow rate.
The extent of ion exchange is a function of the concentration of salts in the blood fluid and of the natraemia of the patient""s blood fluid. In other words, the quantity of salts transferred to the patient is determined by setting the concentration of ions of the dialysate and depends on the ion concentration and on the conditions of the blood fluid. The concentration of the dialysate is measured by determining the conductivity of the dialysate and is monitored during the dialysis treatment.
In less recent dialysis machines, the values of the weight loss in unit time and of the conductivity of the dialysate were kept constant throughout the treatment and were kept relatively low owing to the fact that the patient was unable to tolerate high values, and in consequence the dialysis treatments were extremely long.
The newer dialysis machines are provided with devices for setting up the treatment, in which the values of the weight loss in unit time and of the concentration of salts in the dialysate are set in such a way that they vary as a function of time. This innovation in the field of dialysis machines occurred as a result of research in which it was found that a high weight loss in unit time can be tolerated well by an average patient in the initial stage of treatment, whereas the critical stage with regard to the weight loss in unit time is the final stage of treatment, during which the patient has already lost a large part of the weight, in the form of blood fluid, and is able to tolerate a weight loss in unit time that is relatively low compared with the initial weight loss in unit time. Furthermore, research has also shown that the patient""s receptiveness to the administration of salts in the form of ions is greater in the final stage of treatment compared with the patient""s receptiveness in the initial stage of the treatment. Thus, the data setting devices of the newest machines have adapted to the innovations introduced by medical research and make it possible to define both the function of the weight loss in unit time as a function of time, and the function of the conductivity of the solution of dialysate as a function of time.
Existing devices for setting up a dialysis treatment are based on various methods, some of which envisage the introduction of data on weight loss in unit time for a series of successive intervals of time of the treatment, so that a histogram is substantially defined. In the same way, conductivity data are introduced for a series of time intervals so as to define a histogram. Determination of a histogram makes it possible to define the parameters of the dialysis treatment with increasing precision as the time intervals become shorter, so that the dialysis treatment can be tailored very accurately to the requirements of a given patient. However, these methods require the input of a value for each bar of the histogram, and for this reason it takes a relatively long time to set up the dialysis treatment.
Other less refined methods envisage the setting of only the initial values and final values of weight loss in unit time and of the conductivity of the dialysate solution and the duration of the dialysis treatment and constantly varying the weight loss in unit time and the conductivity between the initial value and the final value. The setting-up time is much shorter for these methods, but they do not permit the setting up of optimum treatments for each patient.
The aim of the present invention is to provide a method of setting up a dialysis treatment in a dialysis machine that does not have the disadvantages of the prior art and, in particular, is accurate, increases the efficiency of the treatment and at the same time can be implemented easily and quickly.
According to the present invention, a method is provided for setting up a dialysis treatment in a dialysis machine comprising the steps of:
determining the conditions (U0, TWL, DT) of a dialysis treatment adapted to a specific patient;
determining a first function (U(t)) of a first quantity (U) characterizing the dialysis treatment as a function of time (t), the first function (U(t)) satisfying the conditions (U0, TWL, DT) of the dialysis treatment and corresponding to a curve having a defined shape;
determining a second function (C(t)) of a second quantity (C) characterizing the dialysis treatment, the second function (C(t)) being correlated with the first function (U(t)) by constants (M, N) determined experimentally and the second function (U(t)) corresponding to a curve having a shape of the same kind as the shape as the first curve.
According to the present invention, once the function of the first quantity has been set, the function of the second quantity is determined automatically, greatly reducing the time for setting up the dialysis treatment.